Mutation

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Mutation

Higher Biology

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Mutation

Change in structure or amount of an organism’s genetic material

Change in genotype produces change in phenotype = mutant

2 types of mutation

Chromosome mutation

Change in structure of one chromosome

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Chromosome mutations

Change in chromosome number

Non-disjunction in meiosis

Non-disjunction of sex chromosomes

Complete non-disjunction and polyploidy

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Non-disjunction during meiosis

Spindle fibre fails during meiosis

Members of one pair of homologous chromosomes fail to become separated

2 gametes receive extra copy of affected chromosome

2 gametes lack that chromosome

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Down’s Syndrome

Non-disjunction in chromosome 21

Occurs in human egg mother cell

One or more abnormal eggs formed (n = 24)

Fertilised by normal sperm (n = 23)

Formation of abnormal zygote (2n = 47)

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Non dis-junction of sex chromosomes

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Turner’s syndrome

Gamete with no sex chromosomes fuses with normal X gamete

Zygote has chromosome complement 2n = 45

Individuals are female and short in stature

Infertile because ovaries haven’t developed normally

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Klinefelter’s syndrome

XX egg fertilised by normal Y sperm

or

Normal X egg is fertilised by an XY sperm

Zygote has chromosome complement 2n = 47 (44 + XXY)

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Always male

Normally infertile

Cannot produce sperm

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Complete non-disjunction and polyploidy